The present invention relates generally to gas generators and more particularly to a disposable CO.sub.2 gas generator which utilizes chemical reactants to generate the CO.sub.2 gas.
Conventional CO.sub.2 gas cylinders are heavy, relatively expensive and available only as returnable, refillable packages. Since such cylinders are under very high pressure, handling requires appropriate care.
With the trend toward mini-sized and home-dispensers for soft-drinks, where the syrup-packaging is generally one-way, it is logistically attractive to make one-way CO.sub.2 packaging also available. Moreover, certain conventional distribution channels, such as supermarket stores, could only be effectively exploited if one-way packaging were available. An additional factor is that lay dispenser users are understandably nervous of handling high-pressure gas cylinders. High pressure CO.sub.2 capsules, generally containing about 8 g CO.sub.2, are already available, but these are expensive and restricted in practical capacity to a limit of around 16-20 g. They do not, therefore, represent a solution, since such quantities are barely sufficient for carbonating 2 liters of beverage without reckoning the considerable additional CO.sub.2 quantities needed for propulsion of the beverage in the dispenser.
Inexpensive, light-weight, unpressurized or moderately pressurized CO.sub.2 packaging can therefore provide a whole scope of new business opportunities with respect to small-sized dispensers designed for non-professional users.
This invention is directed to two main objectives which are not presently met with state of the art apparatus: first, to provide a disposable alternative to the conventional high pressure gas cylinder, utilized, for example, in pre-mix beverage dispensers suitable for home use, and second to provide a miniature self-pressure controlling source for such application as pressurizing the head space of beverage bottles and aerosol cans.
Clearly, if a disposable device is to be acceptable in practice for home use, it must be safe to use, at least as easy and convenient as a gas cylinder, and provide acceptable economics. This is a very exacting requirement, since gas cylinders are generally very safe, require only one single coupling-up action by the user, who does not need any special knowledge, and are reusable almost indefinitely. Known devices, which call for a series of manipulations by the user, are unacceptable since they can never provide an adequate substitute for a single-manipulation gas cylinder. Even two manipulations are inconvenient in comparison with the existing alternative and are also inherently unsafe, because an unsophisticated user can mistakenly use the wrong sequence. Moreover, heavy, complicated devices, may achieve the required convenience and safety aspects, but fail to meet the economic requirements.
To provide a miniature self-pressure controlling source of gas for such applications as aerosols or beverage bottles comprises a task which is quite different from the first since the first objective involves a relatively large gas supply while the second implies the capability of miniaturizing a self-controlled gas supply source. The second objective, moreover, does not provide an alternative to an existing conventional system, but rather provides something for low-boiling point gases such as CO.sub.2, which is currently not available at all.
Gas cylinders, such as used for supplying CO.sub.2 to carbonated beverage dispensers, must support very high pressures and are therefore heavy, expensive, and only suitable as refillable non-disposable containers. In many applications, a gas supply in an inexpensive disposable package would be of great benefit, but such a device would have to circumvent the need to store gas at high pressure, since this inevitably implies heavy-walled expensive vessels, defeating the disposability objective. The present invention resolves this problem by generating gas on demand at a pre-determined controlled pressure.
For pressurizing the head-space of small containers, e.g. aerosols, beverage bottles, soda syphons, etc., two basic methods have hitherto been available. First, a liquid close to its boiling point at normal temperatures has been used, for example, in aerosol containers. However, this method involves using chemicals having doubtful health and environmental properties. Secondly, containers have been known to be pressurized by a relatively safe permanent gas, such as air to CO.sub.2, but this has required high pressures and doubtful safety as well as economics. A gas source, which maintains itself at reasonably constant pressure, responds to demand and can be provided by a device, which is small enough to be fitted into small containers, would provide a solution to this problem, since CO.sub.2 can be used to fill the headspace without the attendant high-pressure penalties.
A well known device originally produced for laboratory use is referred to as a Kipps apparatus. However, this equipment can only produce gas at pressures of a few mm Hg and is not portable in its fully loaded state. Furthermore, it is not in a form which can be disposable. It also requires operation by a trained user. It is, therefore, neither compact nor convenient for use outside a laboratory. A Kipps apparatus, however, can be filled with its solid reagent, and in the absence of the liquid reagent, can be portable. Several other known devices do use a Kipps-like principle and obtain a portability feature, simply by requiring that the user adds the liquid reagent on site. This, however, is inconvenient.
Still other devices recognize the fact that it is difficult to control the gas production on demand and, at the same time, make the system portable and suitable for any chosen gas pressure. These devices obviate the problem by employing a single-step reaction, i.e. a reaction in which all the chemicals are mixed and give up their total gas content in a single operation. But such devices cannot be connected to conventional gas users with continuous gas demand, such as beverage dispensers. In effect, the gas produced by the single-step reaction needs a gas cylinder to store it, so the purpose is defeated. Moreover, most of these devices also require manipulation by the user, usually the addition of water.